Advanced compatible polymer wood fiber composite

ABSTRACT

The invention relates to a composite pellet comprising a thermoplastic polymer and wood fiber composite that can be used in the form of a linear extrudate or thermoplastic pellet to manufacture structural members. The fiber can be modified to increase compatibility. The polymer and wood fiber composite may contain an intentional recycle of a waste stream which can comprise adhesive, paint, preservative, or other chemical waste stream common in the wood-window or door manufacturing process. The initial mixing step before extrusion of the composite material insures substantial mixing and melt contact between molten polymer and wood fiber. The extruded pellet comprises a consistent proportion of polymer, wood fiber and water.

"This application is a Continuation of application Ser. No. 08/779,688,filed Jan. 7, 1997, now abandoned, which application(s) is a divisionalapplication of Ser. No. 08/476,192, filed Jun. 7, 1995, now abandoned,which is a continuation-in-part application of U.S. Ser. No. 08/224,396,filed Apr. 7, 1994, now abandoned, which is a continuation applicationof U.S. Ser. No. 07/938,364, filed Aug. 31, 1992, now abandoned, whichapplication(s) are incorporated herein by reference."

FIELD OF THE INVENTION

The invention relates to compatible composite thermoplastic materialsused for the fabrication of structural members. The thermoplasticmaterials comprise a continuous phase of polyvinyl chloride having adiscontinuous phase of a cellulosic fiber. The composite material ismaintained thermoplastic throughout its useful life by avoiding the useof any substantial concentration of crosslinking agents that wouldeither crosslink cellulosic fibers, polymer molecules or cellulosicfiber to polymer. The physical properties of the thermoplastic materialare improved by increasing polymer-fiber compatibility, i.e. thetendency of the polymer and fiber to mix. The improved mixing tendenciesimproves the coatability of the fiber by polymer, increases the degreethe polymer wets the fiber in the melt stage and substantially increasesthe engineering properties of the materials as a whole. In particular,the improved engineering properties include increased tensile strengthwhen compared to immodified materials (without a compatibilizingcomposition). The improved engineering properties permit the manufactureof improved structural members. Such members can be any structural unit.Preferably the members are for use in windows and doors for residentialand commercial architecture. More particularly, the invention relates toan improved composite material adapted to extrusion or injection moldingprocesses for forming structural members that have improved propertieswhen used in windows and doors. The composite materials of the inventioncan be made to manufacture structural components such as rails, jambs,stiles, sills, tracks, stop and sash, nonstructural trim elements suchas grid, cove, bead, quarter round, etc.

BACKGROUND OF THE INVENTION

Conventional window and door manufacture has commonly used wood andmetal components in forming structural members. Commonly, residentialwindows are manufactured from milled wood products that are assembledwith glass to form typically double hung or casement units. Wood windowswhile structurally sound, useful and well adapted for use in manyresidential installations, can deteriorate under certain circumstances.Wood windows also require painting and other periodic maintenance.Wooden windows also suffer from cost problems related to theavailability of suitable wood for construction. Clear wood products areslowly becoming more scarce and are becoming more expensive as demandincreases. Metal components are often combined with glass and formedinto single unit sliding windows. Metal windows typically suffer fromsubstantial energy loss during winter months.

Extruded thermoplastic materials have been used in window and doormanufacture. Filled and unfilled thermoplastics have been extruded intouseful seals, trim, weatherstripping, coatings and other windowconstruction components. Thermoplastic materials such as polyvinylchloride have been combined with wood members in manufacturingPERMASHIELD® brand windows manufactured by Andersen Corporation for manyyears. The technology disclosed in Zanini, U.S. Pat. Nos. 2,926,729 and3,432,883, have been utilized in the manufacturing of plastic coatingsor envelopes on wooden or other structural members. Generally, thecladding or coating technology used in making PERMASHIELD® windowsinvolves extruding a thin polyvinyl chloride coating or envelopesurrounding a wooden structural member.

Recent advances have made a polyvinyl chloride/cellulosic fibercomposite material useful in the manufacture of structural members forwindows and doors. Puppin et al., U.S. Pat. No. 5,406,768 comprise acontinuous phase of polyvinyl chloride and a particular wood fibermaterial having preferred fiber size and aspect ratio in a thermoplasticmaterial that provides engineering properties for structural members andfor applications in window and door manufacture. These thermoplasticcomposite materials have become an important part of commercialmanufacture of window and door components. While these materials aresufficiently strong for most structural components used in window anddoor manufacture, certain components require added stiffness, tensilestrength, elongation at break or other engineering property not alwaysprovided by the materials disclosed in Puppin et al.

We have examined the modification of thermoplastic materials in thecontinuous polymer phase, the modification of the cellulosic materialsin the discontinuous cellulosic phase for improving the structuralpolymers of these composite materials. The prior art has recognized thatcertain advantages can be obtained by a judicious modification of thematerials. For example, a number of additives are known for use in boththermoplastic and cellulosic materials including molding lubricants,polymer stabilizers, pigments, coatings, etc.

The prior art contains numerous suggestions regarding polymer fibercomposites. Gaylord, U.S. Pat. Nos. 3,765,934, 3,869,432, 3,894,975,3,900,685, 3,958,069 and Casper et al., U.S. Pat. No. 4,051,214 teach abulk polymerization that occurs in situ between styrene and maleicanhydride monomer combined with wood fiber to prepare a polymer fibercomposite. Segaud, U.S. Pat. No. 4,528,303 teaches a compositecomposition containing a polymer, a reinforcing mineral filler and acoupling agent that increases the compatibility between the filler andthe polymer. The prior art also recognizes modifying the fiber componentof a composite. Hamed, U.S. Pat. No. 3,943,079 teaches subjectingunregenerated cellulose fiber to a shearing force resulting in mixingminor proportions of a polymer and a lubricant material with the fiber.Such processing improves fiber separation and prevents agglomeration.The processing with the effects of the lubricant tends to enhancereceptiveness of the fiber to the polymer reducing the time required formixing. Similarly, Coran et al., U.S. Pat. No. 4,414,267 teaches atreatment of fiber with an aqueous dispersion of a vinyl chloridepolymer and a plasticizer, the resulting fibers contain a coating ofpolyvinyl chloride and plasticizer and can be incorporated into thepolymer matrix with reduced mixing energy. Beshay, U.S. Pat. Nos.4,717,742 and 4,820,749 teach a composite material containing acellulose having grafted silane groups. Raj et al., U.S. Pat. No.5,120,776 teach cellulosic fibers pretreated with maleic or phthalicanhydride to improve the bonding and dispersibility of the fiber in thepolymer matrix. Raj et al. teach a high density polyethylene chemicaltreated pulp composite. Hon, U.S. Pat. No. 5,288,772 discloses fiberreinforced thermoplastic made with a moisture pretreated cellulosicmaterial such as discarded newspapers having a lignant content. Kokta etal., "Composites of Poly(Vinyl Chloride) and Wood Fibers. Part II.Effect of Chemical Treatment", Polymer Composites, April 1990, Volume11, No. 2, teach a variety of cellulose treatments. The treatmentsinclude latex coating, grafting with vinyl monomers, grafting with acidsor anhydrides, grafting with coupling agents such as maleic anhydride,abietic acid (See also Kokta, U.K. Application No. 2,192,397). Beshay,U.S. Pat. No. 5,153,241 teaches composite materials including a modifiedcellulose. The cellulose is modified with an organo titanium couplingagent which reacts with and reinforces the polymer phase. Similarly, themodification of the thermoplastic is also suggested in metalpolypropylene laminates, crystallinity of polypropylene has beenmodified with an unsaturated carboxylic acid or derivative thereof. Suchmaterials are known to be used in composite formation.

Maldas et al. in "Performance of Hybrid Reinforcements in PVCComposites: Part I and Part III", Journal of Testing and Evaluation,Vol. 21, No. 1, 1993, pp. 68-72 and Journal of Reinforced Plastics andComposites, Volume II, October 1992, pp. 1093-1102 teach small moleculemodification of filler such as glass, mica, etc. in PVC composites. Noimprovement in physical properties are demonstrated as a result ofsample preparation and testing. Maldas and Kokta, "Surface modificationof wood fibers using maleic anhydride and isocyanate as coatingcomponents and their performance in polystyrene composites", JournalAdhesion Science Technology, 1991, pp. 1-14 show polystyrene flourcomposites containing a maleic anhydride modified wood flour. A numberof publications including Kokta et al., "Composites of PolyvinylChloride-Wood Fibers. III: Effect of Silane as Coupling Agent", Journalof Vinyl Technolocy, Vol. 12, No. 3, September 1990, pp. 142-153disclose modified polymer (other references disclosed modified fiber) inhighly plasticized thermoplastic composites. Additionally, Chahyadi etal., "Wood Flour/Polypropylene Composites: Influence of MaleatedPolypropylene and Process and Composition Variables on MechanicalProperties", International Journal Polymeric Materials, Volume 15, 1991,pp. 21-44 discuss polypropylene composites having polymer backbonemodified with maleic anhydride.

Accordingly, a substantial need exists for an improved thermoplasticcomposite material that can be made of polymer and wood fiber with anoptional, intentional recycle of a waste stream. A further need existsfor an improved thermoplastic composite material that can be extrudedinto a shape that is a direct substitute for the equivalent milled shapein a wooden or metal structural member. This need requires athermoplastic composite with creep resistance, improved heat distortiontemperature having a coefficient of thermal expansion that approximateswood, a material that can be extruded into reproducible stabledimensions, a high compressive strength, a low thermal transmissionrate, an improved resistance to insect attack and rot while in use and ahardness and rigidity that permits sawing, milling, and fasteningretention comparable to wood members. Further, companies manufacturingwindow and door products have become significantly sensitive to wastestreams produced in the manufacture of such products. Substantialquantities of wood waste including wood trim pieces, sawdust, woodmilling by-products; recycled thermoplastic including recycled polyvinylchloride, has caused significant expense to window manufacturers.Commonly, these materials are either burned for their heat value inelectrical generation or are shipped to qualified landfills fordisposal. Such waste streams are contaminated with substantialproportions of hot melt and solvent-based adhesives, waste thermoplasticsuch as polyvinyl chloride, paint, preservatives, and other organicmaterials. A substantial need exists to find a productiveenvironmentally compatible use for such waste streams to avoid returningthe materials into the environment in an environmentally harmful way.Such recycling requires that the recycled material remains largelythermoplastic. Lastly a substantial need exists to improve polyvinylchloride-cellulosic composites for use in high stress or high loadbearing applications.

BRIEF DISCUSSION OF THE INVENTION

We have found that the problems relating to polymer-fiber composites canbe solved by forming compatible thermoplastic/fiber composite from amodified polymer or a modified wood fiber, or both. An increase incompatibility between polymer and fiber can be characterized by ameasurable increase (outside standard deviation) in tensile strength orapplied tensile strength at point of yield of material. The improvedcompatibility of the materials improves wetting and incorporation offiber into polymer, increasing reinforcement and a resulting improvementin tensile strength.

For the purpose of this application, the term "modified polymer(derivative polymer)" indicates a polymeric material having side groupsor moieties deliberately introduced onto the polymer backbone orcopolymerized into the polymer backbone that increase the tendency ofthe polymer to associate with or wet the fiber surface. Typically, suchmodifications introduce pendant groups onto the polymer that formhydrogen bonds with the cellulosic material. Similarly, the cellulosecan be modified or derivative. The term "derivatized or modifiedcellulose" for purposes of this invention include reacting the cellulosewith a reagent that forms a derivative on either a primary or secondaryhydroxyl of the cellulosic material. The hydroxyl reactive reagentcontains a substituent group of similar polarity to the polymer materialused in an ultimate composite. For the purpose of this application, theterm "compatibility with a thermoplastic polymer" can be characterizedby differential scanning calorimetry (DSC) data and by measuring surfaceenergy using a goniometer device. In examining compatibility using adifferential scanning calorimeter, the calorimetry of a separate polymerphase and a modified cellulose phase or the cellulose modifier reagentcan be measured with DSC equipment. After the materials are mixed,compatibility can be shown in a DSC scan by showing differences in theT_(g) peaks. Compatible materials have modified T_(g) 's, fullycompatible materials will form a single T_(g) peak in the scan. To matcha polymer with a reagent or reagent group, measuring the surface energyof the materials using a goniometer will produce a surface energyquantity. Similar quantities will suggest compatibility.

The polymer compatible functional group on the cellulose naturallyassociates with the polymer using van der Waals' forces causing anincreased compatibility, mixing or wetting of the polymer with thefiber.

Similarly, both the polymer and the cellulosic material can bederivatized with functional groups that increase the polymer fibercompatibility. Further, the functional groups can have moieties on thefunctional group that are compatible with the corresponding moiety. Theincreased compatibility of polymer and fiber after modification can beobtained by measuring the DSC properties or surface energy of themodified polymer/fiber, the polymer/modified fiber or the modifiedpolymer/modified fiber when compared to the polymer/fiber materialalone. Such materials with increased compatibility have improvedthermodynamic properties and reduced energy of mixing.

The resulting modified materials remain completely thermoplastic becausethey are substantially free of any substantial crosslinking offiber-to-fiber or polymer-to-fiber. Further, the material oncemanufactured can be extruded in the form of a thermoplastic pellet whichcan then be subject to heat and pressure and molded using eitherextrusion technology or thermoforming technology into window and doorstructural members. The wood fiber preferably comprises sawdust ormilling byproduct waste stream from milling wooden members in windowmanufacture and can be contaminated with substantial proportions of hotmelt adhesive, paint, solvent or adhesive components, preservatives,polyvinyl chloride recycle pigment, plasticizers, etc. We have foundthat the PVC and wood fiber composite can be manufactured intoacceptable substitutes for wooden members if the PVC and wood materialcontains less than about 10 wt-%, preferably less than 3.5% water basedon pellet weight. Water is removed by degassing (removing water vapor)during melt processing of the composite. The compositions can achieve,in a final product, high modulus, improved creep resistance, improvedheat distortion temperature, high compressive strength, reproducible,stable dimensions, a superior modulus and elasticity. We have also foundthat the successful manufacture of structural members for windows anddoors requires the preliminary manufacture of the polyvinyl chloridewood fiber composite in the form of a pellet wherein the materials areintimately mixed and contacted in forming the pellet prior to theextrusion of the members from the pellet material. We have found thatthe intimate mixing of polyvinyl chloride and wood fiber of increasedcompatibility (and optionally waste) in the manufacture of the pelletprocess with associated control of moisture content produces apelletized product that is uniquely adapted to the extrusion manufactureof PVC/wood fiber components and achieves the manufacture of a usefulwood replacement product. The materials of the invention are free of aneffective quantity of a plasticizer. Such materials can only reduce theultimate mechanical strength of the material. Further the material isformulated with proportions of materials that remain fully thermoplasticand recyclable in normal melt processing.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to the use of a modified polyvinyl chloride, amodified wood fiber or both, in a composite material. The preferredmaterial has a controlled water content. The material is preferably madein the form of a pelletized compatible material wherein the wood fiberis intimately contacted and wetted by the organic materials due toincreased compatibility. The intimate contact and wetting between thecomponents in the pelletizing process ensures high quality physicalproperties in the extruded composite materials after manufacture.

Modified Polymer

The preferred material is a polymer comprising vinyl chloride. Amodified polymer, as defined below, can be used with modified orunmodified cellulose. Unmodified polymer can be used only with amodified adhesive fiber.

Polyvinyl chloride is a common commodity thermoplastic polymer. Vinylchloride monomer is made from a variety of different processes such asthe reaction of acetylene and hydrogen chloride and the directchlorination of ethylene. Polyvinyl chloride is typically manufacturedby the free radical polymerization of vinyl chloride resulting in auseful thermoplastic polymer. After polymerization, polyvinyl chlorideis commonly combined with thermal stabilizers, lubricants, plasticizers,organic and inorganic pigments, fillers, biocides, processing aids,flame retardants and other commonly available additive materials.Polyvinyl chloride can also be combined with other vinyl monomers in themanufacture of polyvinyl chloride copolymers. Such copolymers can belinear copolymers, branched copolymers, graft copolymers, randomcopolymers, regular repeating copolymers, heteric copolymers and blockcopolymers, etc. Monomers that can be combined with vinyl chloride toform vinyl chloride copolymers include a acrylonitrile; alpha-olefinssuch as ethylene, propylene, etc.; chlorinated monomers such asvinylidene dichloride, acrylate monomers such as acrylic acid,methylacrylate, methylmethacrylate, acrylamide, hydroxyethyl acrylate,and others; styrenic monomers such as styrene, alphamethyl styrene,vinyl toluene, etc.; vinyl acetate; and other commonly availableethylenically unsaturated monomer compositions.

Such monomers can be used in an amount of up to but less than about 50mol-%, the balance being vinyl chloride. Polymer blends or polymeralloys can also be useful in manufacturing the pellet or linearextrudate of the invention. Such alloys typically comprise two misciblepolymers blended to form a uniform composition. Scientific andcommercial progress in the area of polymer blends has lead to therealization that important physical property improvements can be madenot by developing new polymer material but by forming miscible polymerblends or alloys. A polymer alloy at equilibrium comprises a mixture oftwo amorphous polymers existing as a single phase of intimately mixedsegments of the two macro molecular components. Miscible amorphouspolymers form glasses upon sufficient cooling and a homogeneous ormiscible polymer blend exhibits a single, composition dependent glasstransition temperature (T_(g)). Immiscible or non-alloyed blend ofpolymers typically displays two or more glass transition temperaturesassociated with immiscible polymer phases. In the simplest cases, theproperties of polymer alloys reflect a composition weighted average ofproperties possessed by the components. In general, however, theproperty dependence on composition varies in a complex way with aparticular property, the nature of the components (glassy, rubbery orsemi-crystalline), the thermodynamic state of the blend, and itsmechanical state whether molecules and phases are oriented. Polyvinylchloride forms a number of known polymer alloys including, for example,polyvinyl chloride/nitrile rubber; polyvinyl chloride and relatedchlorinated copolymers and terpolymers of polyvinyl chloride orvinylidene dichloride; polyvinyl chloride/alphamethylstyrene-acrylonitrile copolymer blends; polyvinyl chloride/polyethylene;polyvinyl chloride/chlorinated polyethylene and others.

The primary requirement for the substantially thermoplastic polymericmaterial is that it retain sufficient thermoplastic properties to permitmelt blending with wood fiber, permit formation of linear extrudatepellets, and to permit the composition material or pellet to be extrudedor injection molded in a thermoplastic process forming the rigidstructural member. Polyvinyl chloride homopolymers copolymers andpolymer alloys are available from a number of manufacturers including B.F. Goodrich, Vista, Air Products, Occidental Chemicals, etc. Preferredpolyvinyl chloride materials are polyvinyl chloride homopolymer having amolecular weight (Mn) of about 90,000±50,000, most preferably about88,000±10,000.

Modifications

The polyvinyl chloride material is modified to introduce pendant groupsthat can form hydrogen bonds with the cellulosic hydroxyl groups.Cellulose molecules are known to be polymers of glucose with varyingbranching and molecular weight. Glucose molecules contain both secondaryand primary hydroxyl groups and many such groups are available forhydrogen bonding.

The modified polyvinyl chloride comprises either a polymer comprisingvinyl chloride and a second monomer having functional groups that arecapable of forming hydrogen bonds with cellulose. Further, the modifiedpolymer can comprise a polymer comprising vinyl chloride and optionallya second monomer that is reacted with the modifying reagent that canform substituents having hydrogen bonding functional groups.

Polymer Modifications

The polyvinyl chloride polymer material can be modified either bygrafting onto the polymer backbone a reactive moiety compatible with thecellulose or by incorporating into the polymer backbone, bycopolymerization techniques, functional groups that can increase polymercompatibility. It should be clearly understood that the PVC cellulosicfiber compatibility is relatively good. Wood fiber and polyvinylchloride polymer will mix under conditions achievable in modernextrusion equipment. However, the compatibility of long chainmodifications to the cellulosic polymer material provides significantlyenhanced tensile strength.

Representative examples of monomers that can be included as a minorcomponent (less than 50 mol-%) in a polyvinyl chloride copolymer includevinyl alcohol (hydrolyzed polyvinyl acetate monomer), maleic anhydridemonomer, glycidyl methacrylate, vinyl oxazolines, vinyl pyrrolidones,vinyl lactones, and others. Such monomers when present at the preferredconcentration (less than 10 mol-%, preferably less than 5 mol-%) reactcovalently with cellulose hydroxyl groups and form associative bondswith cellulosic hydroxyl groups resulting in increased compatibility butare not sufficiently reacted to result in a crosslinked material. Thepolyvinyl chloride polymer material can be grafted with a variety ofreactive compositions. In large part, the reactive species has a primaryor secondary nitrogen, an oxygen atom, or a carboxyl group that can bothcovalently bond (to a small degree) and form hydroxyl groups withcellulosic materials. Included within the useful reactive species areN-vinyl pyrrolidone, N-vinyl pyridine, N-vinyl pyrimidine, polyvinylalcohol polymers, unsaturated fatty acids, acrylic acid, methacrylicacid, reactive acrylic oligomers, reactive amines, reactive amides andothers. Virtually any reactive or grafting species containing a hydrogenbonding atom can be used as a graft reagent for the purposes of thisinvention.

Modified Fiber

Wood fiber, in terms of abundance and suitability can be derived fromeither soft woods or evergreens or from hard woods commonly known asbroad leaf deciduous trees. Soft woods are generally preferred for fibermanufacture because the resulting fibers are longer, contain highpercentages of lignin and lower percentages of hemicellulose than hardwoods. While soft wood is the primary source of fiber for the invention,additional fiber make-up can be derived from a number of secondary orfiber reclaim sources including bamboo, rice, sugar cane, and recycledfibers from newspapers, boxes, computer printouts, etc.

However, the primary source for wood fiber of this invention comprisesthe wood fiber by-product of sawing or milling soft woods commonly knownas sawdust or milling tailings. Such wood fiber has a regularreproducible shape and aspect ratio. The fibers based on a randomselection of about 100 fibers are commonly at least 3 mm in length, 1 mmin thickness and commonly have an aspect ratio of at least 1.8.Preferably, the fibers are 1 to 10 mm in length, 0.3 to 1.5 mm inthickness with an aspect ratio between 2 and 7, preferably 2.5 to 6.0.The preferred fiber for use in this invention are fibers derived fromprocesses common in the manufacture of windows and doors. Wooden membersare commonly ripped or sawed to size in a cross grain direction to formappropriate lengths and widths of wood materials. The by-product of suchsawing operations is a substantial quantity of sawdust. In shaping aregular shaped piece of wood into a useful milled shape, wood iscommonly passed through machines which selectively removes wood from thepiece leaving the useful shape. Such milling operations producessubstantial quantities of sawdust or mill tailing by-products. Lastly,when shaped materials are cut to size and mitered joints, butt joints,overlapping joints, mortise and tenon joints are manufactured frompre-shaped wooden members, substantial waste trim is produced. Suchlarge trim pieces are commonly cut and machined to convert the largerobjects into wood fiber having dimensions approximating sawdust or milltailing dimensions. The wood fiber sources of the invention can beblended regardless of particle size and used to make the composite. Thefiber stream can be pre-sized to a preferred range or can be sized afterblending. Further, the fiber can be pre-pelletized before use incomposite manufacture.

Such sawdust material can contain substantial proportions of wastestream by-products. Such by-products include waste polyvinyl chloride orother polymer materials that have been used as coating, cladding orenvelope on wooden members; recycled structural members made fromthermoplastic materials; polymeric materials from coatings; adhesivecomponents in the form of hot melt adhesives, solvent based adhesives,powdered adhesives, etc.; paints including water based paints, alkydpaints, epoxy paints, etc.; preservatives, anti-fungal agents,anti-bacterial agents, insecticides, etc., and other waste streamscommon in the manufacture of wooden doors and windows. The total wastestream content of the wood fiber materials is commonly less than 25 wt-%of the total wood fiber input into the polyvinyl chloride wood fiberproduct. Of the total waste recycle, approximately 10 wt-% of that cancomprise a vinyl polymer commonly polyvinyl chloride. Commonly, theintentional recycle ranges from about 1 to about 25 wt-%, preferablyabout 2 to about 20 wt-%, most commonly from about 3 to about 15 wt-% ofcontaminants based on the sawdust.

Modifications

The modified cellulosic material of the invention that can be combinedwith polymer material to form the preferred composite material comprisesa cellulosic fiber having surface moieties containing substituent groupshaving a polarity and composition that matches the polyvinyl chloridematerial. In a preferred mode the chemical modifier comprises long chaingroups that can entangle or associate with the polymer to increasecompoatability. Such chains are typically polymeric but can also be long(C₆₋₃₆) aklyl groups.

As discussed above, compatible polymeric species that can associate withpolyvinyl chloride polymers in improving compatibility can be foundusing either differential scanning calorimetry or surface energy(goniometer) data. Examples of compatible polymer species that can begrafted onto a cellulosic molecule for increasing compatibility includeacrylonitrile butadiene styrene polymers, maleic anhydride butadienestyrene polymers, chlorinated polyethylene polymers, styreneacrylonitrile polymers, alpha styrene acrylonitrile polymers, polymethylmethacrylate polymers, ethylene vinyl acetate polymers, natural rubberpolymers, a variety of thermoplastic polyurethane polymers, styrenemaleic anhydride polymers, synthetic rubber elastomers, polyacrylicimidepolymers, polyacrylamide polymers, polycaprolactone polymers,poly(ethylene-adipate). Such polymeric groups can be reacted with otherreactive species to form on the polymeric backbone a group reactive witha cellulosic hydroxyl group to result in a modified cellulose material.Such functional groups include carboxylic anhydrides, epoxides(oxirane), carboxylic acids, carboxylic acid chlorides, isocyanate,lactone, alkyl chloride, nitrile, oxazoline, azide, etc.

Pellet

The polyvinyl chloride and wood fiber can be combined and formed into apellet using a thermoplastic extrusion processes. Wood fiber, modifiedor unmodified, can be introduced into pellet making process in a numberof sizes. We believe that the wood fiber should have a minimum size oflength and width of at least 1 mm because wood flour tends to beexplosive at certain wood to air ratios. Further, wood fiber ofappropriate size of a aspect ratio greater than 1 tends to increase thephysical properties of the extruded structural member. However, usefulstructural members can be made with a fiber of very large size. Fibersthat are up to 3 cm in length and 0.5 cm in thickness can be used asinput to the pellet or linear extrudate manufacturing process. However,particles of this size do not produce highest quality structural membersor maximized structural strength. The best appearing product withmaximized structural properties are manufactured within a range ofparticle size as set forth below. Further, large particle wood fiber anbe reduced in size by grinding or other similar processes that produce afiber similar to sawdust having the stated dimensions and aspect ratio.One further advantage of manufacturing sawdust of the desired size isthat the material can be pre-dried before introduction into the pelletor linear extrudate manufacturing process. Further, the wood fiber canbe pre-pelletized into pellets of wood fiber with small amounts ofbinder if necessary.

During the pelletizing process for the composite pellet, the polyvinylchloride in an appropriate modification if modified and wood fiber areintimately contacted at high temperatures and pressures to insure thatthe wood fiber and polymeric material are wetted, mixed and extruded ina form such that the polymer material, on a microscopic basis, coats andflows into the pores, cavity, etc., of the fibers. The fibers arepreferably substantially oriented by the extrusion process in theextrusion direction. Such substantial orientation causes overlapping ofadjacent parallel fibers and polymeric coating of the oriented fibersresulting a material useful for manufacture of improved structuralmembers with improved physical properties. The degree of orientation isabout 20%, preferably 30% above random orientation which is about 45 to50%. The structural members have substantially increased strength andtensile modulus with a coefficient of thermal expansion and a modulus ofelasticity that is optimized for window and doors. The properties are auseful compromise between wood, aluminum and neat polymer.

Moisture control is an important element of manufacturing a usefullinear extrudate or pellet. Depending on the equipment used andprocessing conditions, control of the water content of the linearextrudate or pellet can be important in forming a successful structuralmember substantially free of internal voids or surface blemishes. Theconcentration of water present in the sawdust during the formation ofpellet or linear extrudate when heated can flash from the surface of thenewly extruded structural member and can come as a result of a rapidvolatilization, form a steam bubble deep in the interior of the extrudedmember which can pass from the interior through the hot thermoplasticextrudate leaving a substantial flaw. In a similar fashion, surfacewater can bubble and leave cracks, bubbles or other surface flaws in theextruded member.

Trees when cut depending on relative humidity and season can containfrom 30 to 300 wt-% water based on fiber content. After rough cuttingand finishing into sized. lumber, seasoned wood can have a water contentof from 20 to 30 wt-% based on fiber content. Kiln dried sized lumbercut to length can have a water content typically in the range of 8 to12%, commonly 8 to 10 wt-% based on fiber. Some wood source, such aspoplar or aspen, can have increased moisture content while some hardwoods can have reduced water content.

Because of the variation in water content of wood fiber source and thesensitivity of extrudate to water content control of water to a level ofless than 8 wt-% in the pellet based on pellet weight is important.Structural members extruded in non-vented extrusion process, the pelletshould be as dry as possible and have a water content between 0.01 and5%, preferably less than 3.5 wt-%. When using vented equipment inmanufacturing the extruded linear member, a water content of less than 8wt-% can be tolerated if processing conditions are such that ventedextrusion equipment can dry the thermoplastic material prior to thefinal formation of the structural member of the extrusion head.

The pellets or linear extrudate of the invention are made by extrusionof the polyvinyl chloride and wood fiber composite through an extrusiondie resulting in a linear extrudate that can be cut into a pellet shape.The pellet cross-section can be any arbitrary shape depending on theextrusion die geometry. However, we have found that a regular geometriccross-sectional shape can be useful. Such regular cross-sectional shapesinclude a triangle, a square, a rectangle, a hexagonal, an oval, acircle, etc. The preferred shape of the pellet is a regular cylinderhaving a roughly circular or somewhat oval cross-section. The pelletvolume is preferably greater than about 12 mm³. The preferred pellet isa right circular cylinder, the preferred radius of the cylinder is atleast 1.5 mm with a length of at least 1 mm. Preferably, the pellet hasa radius of 1 to 5 mm and a length of 1 to 10 mm. Most preferably, thecylinder has a radius of 2.3 to 2.6 mm, a length of 2.4 to 4.7 mm, avolume of 40 to 100 mm³, a weight of 40 to 130 mg and a bulk density ofabout 0.2 to 0.8 gm/mm³.

We have found that the interaction, on a microscopic level, between theincreased compatible polymer mass and the wood fiber is an importantelement of the invention. We have found that the physical properties ofan extruded member are improved when the polymer melt during extrusionof the pellet or linear member thoroughly wets and penetrates the woodfiber particles improved wetting and penetration is a result ofincreased compatibility. The thermoplastic material comprises anexterior continuous organic polymer phase with the wood particledispersed as a discontinuous phase in the continuous polymer phase. Thematerial during mixing and extrusion obtains an aspect ratio of at least1.1 and preferably between 2 and 4, optimizes orientation such as atleast 20 wt-%, preferably 30% of the fibers are oriented in an extruderdirection and are thoroughly mixed and wetted by the polymer such thatall exterior surfaces of the wood fiber are in contact with the polymermaterial. This means, that any pore, crevice, crack, passage way,indentation, etc., is fully filled by thermoplastic material. Suchpenetration as attained by ensuring that the viscosity of the polymermelt is reduced by operations at elevated temperature and the use ofsufficient pressure to force the polymer into the available internalpores, cracks and crevices in and on the surface of the wood fiber.

During the pellet or linear extrudate manufacture, substantial work isdone in providing a uniform dispersion of the wood into the polymermaterial. Such work produces substantial orientation which when extrudedinto a final structural member, permits the orientation of the fibers inthe structural member to be increased in the extruder directionresulting in improved structural properties.

The pellet dimensions are selected for both convenience in manufacturingand in optimizing the final properties of the extruded materials. Apellet is with dimensions substantially less than the dimensions setforth above are difficult to extrude, pelletize and handle in storage.Pellets larger than the range recited are difficult to introduce intoextrusion or injection molding equipment, and are different to melt andform into a finished structural member.

Composition and Pellet Manufacture

In the manufacture of the composition and pellet of the invention, themanufacture and procedure requires two important steps. A first blendingstep and a second pelletizing step.

During the blending step, the polymer and wood fiber are intimatelymixed by high shear mixing components with recycled material to form apolymer wood composite wherein the polymer mixture comprises acontinuous organic phase and the wood fiber with the recycled materialsforms a discontinuous phase suspended or dispersed throughout thepolymer phase. The manufacture of the dispersed fiber phase within acontinuous polymer phase requires substantial mechanical input. Suchinput can be achieved using a variety of mixing means includingpreferably extruder mechanisms wherein the materials are mixed underconditions of high shear until the appropriate degree of wetting andintimate contact is achieved. After the materials are fully mixed, themoisture content can be controlled at a moisture removal station. Theheated composite is exposed to atmospheric pressure or reduced pressureat elevated temperature for a sufficient period of time to removemoisture resulting in a final moisture content of about 8 wt-% or less.Lastly, the polymer fiber is aligned and extruded into a useful form.

The preferred equipment for mixing and extruding the composition andwood pellet of the invention is an industrial extruder device. Suchextruders can be obtained from a variety of manufacturers includingCincinnati Millicron, etc.

The materials feed to the extruder can comprise from about 30 to 50 wt-%of sawdust including recycled impurity along with from about 50 to 70wt-% of polyvinyl chloride polymer compositions. Preferably, about 35 to45 wt-% wood fiber or sawdust is combined with 65 to 55 wt-% polyvinylchloride homopolymer. The polyvinyl chloride feed is commonly in a smallparticulate size which can take the form of flake, pellet, powder, etc.Any polymer form can be used such that the polymer can be dry mixed withthe sawdust to result in a substantially uniform pre-mix. The wood fiberor sawdust input can be derived from a number of plant locationsincluding the sawdust resulting from rip or cross grain sawing, millingof wood products or the intentional commuting or fiber manufacture fromwaste wood scrap. Such materials can be used directly from theoperations resulting in the wood fiber by-product or the by-products canbe blended to form a blended product. Further, any wood fiber materialalone, or in combination with other wood fiber materials, can be blendedwith waste stream by-product from the manufacturer of wood windows asdiscussed above. The wood fiber or sawdust can be combined with otherfibers and recycled in commonly available particulate handlingequipment.

Polymer and wood fiber are then dry blended in appropriate proportionsprior to introduction into blending equipment. Such blending steps canoccur in separate powder handling equipment or the polymer fiber streamscan be simultaneously introduced into the mixing station at appropriatefeed ratios to ensure appropriate product composition.

In a preferred mode, the wood fiber is placed in a hopper, controlled byweight or by volume, to meter the sawdust at a desired volume while thepolymer is introduced into a similar hopper have a gravametric meteringinput system. The weights are adjusted to ensure that the compositematerial contains appropriate proportions on a weight basis of polymerand wood fiber. The fibers are introduced into a twin screw extrusiondevice. The extrusion device has a mixing section, a transport sectionand melt section. Each section has a desired heat profile resulting in auseful product. The materials are introduced into the extruder at a rateof about 600 to about 4000 pounds of material per hour and are initiallyheated to a temperature of about 215-225° C. In the intake section, thestage is maintained at about 215° C. to 225° C. In the mixing section,the temperature of the twin screw mixing stage is staged beginning at atemperature of about 205-215° C. leading to a final temperature in themelt section of about 195-205° C. at spaced stages. Once the materialleaves the blending stage, it is introduced into a three stage extruderwith a temperature in the initial section of 185-195° C. wherein themixed thermoplastic stream is divided into a number of cylindricalstreams through a head section and extruded in a final zone of 195-200°C. Such head sections can contain a circular distribution (6-8"diameter) of 10 to 500 or more, preferably 20 to 250 orifices having across-sectional shape leading to the production of a regular cylindricalpellet. As the material is extruded from the head it is cut with adouble-ended knife blade at a rotational speed of about 100 to 400 rpmresulting in the desired pellet length.

The following examples were performed to further illustrate theinvention that is explained in detail above. The following informationillustrates the typical production conditions and compositions and thetensile modulus of a structural member made from the pellet. Thefollowing examples and data contain a best mode.

COMPARATIVE EXAMPLES-UNMODIFIED PVC-FIBER COMPOSITE

A Cincinnati millicron extruder with an HP barrel, Cincinnati pelletizerscrews, an AEG K-20 pelletizing head with 260 holes, each hole having adiameter of about 0.0200 inches was used to make the pellet. The inputto the pelletizer comprised approximately 60 wt-% polymer and 40 wt-%sawdust. The polymer material comprises a thermoplastic mixture ofapproximately 100 parts of polyvinyl chloride homopolymer (in. weight of88,000±2000), about 15 parts titanium dioxide, about 2 parts ethylenebis-stearamide wax lubricant, about 1.5 parts calcium stearate, about7.5 parts Rohm & Haas 980 T acrylic resin impact modifier/process aidand about 2 parts of dimethyl tin thioglycolate. The sawdust comprises awood fiber particle containing about 5 wt-% recycled polyvinyl chloridehaving a composition substantially identical to that recited above.

The initial melt temperature in the extruder was maintained between 180°C. and 210° C. The pelletizer was operated at a polyvinylchloride-sawdust composite combined through put of 800 pounds per hour.In the initial extruder feed zone, the barrel temperature was maintainedbetween 215-225° C. In the intake zone, the barrel was maintained at215-225° C., in the compression zone the temperature was maintained atbetween 205-215° C. and in the melt zone the temperature was maintainedat 195-205° C. The die was divided into three zones, the first zone at185-195° C., the second die zone at 185-195° C. and in the final diezone at 195-205° C. The pelletizing head was operated at a settingproviding 100 to 300 rpm resulting in a pellet with a diameter of 5 mmand a length of about 1-10 mm.

    ______________________________________                                        EXPERIMENTAL                                                                  Sample Preparation for Styrene Maleic*                                        Anhydride Compatibilizer Formulation                                                  Composition (parts by weight)                                         Run number                                                                              PVC compound    saw dust SMA                                        ______________________________________                                        1         100             0        0                                          2         100             0        10                                         3         90              10       0                                          4         90              10       10                                         5         75              25       0                                          6         75              25       10                                         7         60              40       0                                          8         60              40       10                                         9         50              50       0                                          10        50              50       10                                         ______________________________________                                         *In the following work the modifier is referred to by these numbers.     

1. SMA used was a random copolymer of styrene and maleic anhydride fromARCO Chemical Company, Dylark 332 with 14% maleic anhydride, MW=190,000

2. VERR40 is a terpolymer of Vinylchloride-vinylacetate-glycidylmethacrylate (82%-9%-9%) with an epoxy functionality of 1.8% by weight

3. Terpolymer used was "Vinyl chloride-vinyl acetate-vinyl alcohol"(91%-3%-6%) from Scientific Polymer Products, Inc., MW=70,000.

4. Epoxy used was Dows' DER332 which is a Diglycidyl bisphenol A epoxy

5. Catalyst used was Triethylene amine from Aldrich Chemical Company

6. ATBN rubber used was Goodrich's "HYCAR 1300X45" which is an "amineterminated butadiene acrylonitrile copolymer

1. Sawdust Preparation

Ponderosa Pine Sawdust ground and sieved to provide 80% 40-60 mesh and<15% fines

Sawdust is dried to <1% moisture

2. PVC Compound

100 parts of Geon Resin 427 and 1 part of a methyltin mercaptide(Advastab TM 181 Methyltin Mercaptide) are blended in a high intensitymixer to temperature of 150° F. 1.7 parts of a fatty acid ester (LoxiolVGE 1884, and 0.4 part of an oxidized polyethylene (AC 629-A) are addedand the PVC compound is mixed for an additional 4 minutes. (StandardMixing procedures)

3. Styrene Maleic Anhydride

The SMA was Dylark 332 from ARCO chemical contains 14-15% maleicanhydride and molecular weight of approximately 170,000

4. 2×5 full factorial matrix

SMA was either 0, or 10 parts

Sawdust was 0, 10, 25, 40, or 50 parts

PVC varied inversely with the sawdust 100, 90, 75, 60, or 50 parts suchthat the PVC and saw dust parts added up to 100 parts

5. Mixing of PVC, Sawdust, and SMA

Mixing of PVC, Sawdust, and SMA was done on a Hobart "dough" mixer.

6. Extrusion

The formulations were fed into a twin screw counter rotating extruderand extruded as a 1"×0.1" strip.

7. Second Pass through Extruder

Strips from #6 above were ground into pellets with a Cumberland grinderand fed into the twin screw extruder for a second time.

Tensile Testing

Tensile testing was performed in accordance with ASTM Method 3039M on anInstron 4505

                                      TABLE 1                                     __________________________________________________________________________                            Tensile Properties                                           Composition (parts by weight)                                                                        % strain @                                      Run number                                                                           PVC compound                                                                          saw dust                                                                           SMA Modulus                                                                             max load                                                                            stress                                    __________________________________________________________________________    1      100     0    0   536,533                                                                             2.772                                           2      100     0    10  494,010                                                                             2.535                                           3      90      10   0   579,925                                                                             2.746                                           4      90      10   10  573,448                                                                             2.452                                           5      75      25   0   829,455                                                                             1.819                                           6      75      25   10  844,015                                                                             1.548                                           7      60      40   0   1,112,819                                                                           1.145                                           8      60      40   10  1,039,749                                                                           1.168                                           9      50      50   0   1,254,213                                                                           0.843                                           10     50      50   10  1,174,936                                                                           0.965                                           __________________________________________________________________________     These data show the chemical modification has no significant impact on        modulus, but has a significant increase in both % strain and in stress        values.                                                                  

Soxhlet Extraction

Five gram samples from test strips were extracted for 24 hours with hottetrahydrofuran to determine percent resin bound to sawdust.

    ______________________________________                                        PVC       WF         SMA        % Retain                                      ______________________________________                                        NNC3      2% M.C.    --         38.83                                         NNC3      2% M.C.    332-10%    43.88                                         NNC3      wet, 40%   --         41.21                                         NNC3      wet, 40%   332-10%    47.25                                         NNC3      wet, 40%   Butadiene-Man                                                                            48.39                                         NNC3      0          SMA332     30.61                                         ______________________________________                                    

These data show that the SMA reacts with and is bonded to the wood fiberto increase compatibility.

Sample Preparation for Vinyl Chloride Vinyl Acetate GlycidylMethacrylate Compatibilizer Formulation

    ______________________________________                                                Composition (parts by weight)                                         Run number                                                                              PVC compound  saw dust VERR-40                                      ______________________________________                                        1         100           0        0                                            2         96            0        4                                            3         90            0        10                                           4         60            40       0                                            5         57.6          40       2.4                                          6         54            40       6                                            ______________________________________                                    

1. Sawdust Preparation

Ponderosa Pine Sawdust ground and sieved to provide 80% 40-60 mesh and<15% fines.

Sawdust is dried to <1% moisture

2. PVC Compound

100 parts of Geon Resin 427 and 2 parts of a methyltin mercaptide(Advastab TM 181 Methyltin Mercaptide) are blended in a high intensitymixer to temperature of 150° F. 0.5 parts of a paraffin wax (XL 165),0.8 parts of an oxidized polyethylene (AC 629-A) are added and the PVCcompound is mixed for an additional 4 minutes (Standard Mixingprocedures)

3. Vinyl Chloride Vinyl Acetate glycidyl methacrylate

The Vinyl Chloride Vinyl Acetate glycidyl methacrylate (82%-9%-9% bymole) was UCAR VERR-40 from Union Carbide Chemicals and Plasticscontains 9% glycidyl methacrylate and comes as a 40% solution in tolueneand methyl ethyl ketone.

4. 2×3 full factorial matrix

VERR-40 was either 0, 4, or 10 parts of the PVC compound based on theweight of the solids.

Sawdust was 0 or 40 parts PVC+the VERR-40 varied inversely with thesawdust 100, or 60, parts such that the PVC+VERR-40 and sawdust partsadded up to 100 parts.

5. Mixing of PVC, Sawdust, and VERR-40

Mixing of PVC, Sawdust, and VERR-40 was done on a Hobart "dough" mixer.

The VERR-40 was diluted with an additional 50 ml acetone and added tothe sawdust first and mixed to provide even dispersion of VERR-40 on thesawdust.

Then the PVC was added with continued mixing.

6. Extrusion

The formulations were fed into a twin screw counter rotating extruderand extruded as a 1"×0.1" strip.

7. Tensile Testing

Tensile testing was performed in accordance with ASTM method D3039 on anInstron 4505

    __________________________________________________________________________                            Tensile Properties                                    Composition (parts by weight) % strain @                                      Run number                                                                          PVC compound                                                                          saw dust                                                                           VERR-40                                                                            Modulus                                                                             max load                                                                            stress                                    __________________________________________________________________________    1     100     0    0    501,236                                                                             3.301 8458.6                                    2     96      0    4    488,245                                                                             2.741 7493.7                                    3     90      0    10   459,835                                                                             2.951 6833                                      4     60      40   0    1,143,393                                                                           0.949 6384.5                                    5     57.6    40   2.4  1,230,761                                                                           0.961 6688.9                                    6     54      40   6    1,273,530                                                                           0.889 6969.3                                    __________________________________________________________________________     These data show significant improvement in stress with no substantial los     in modulus.                                                              

8. Soxhlet Extraction

Five gram samples from test strips were extracted for 24 hours with hottetrahydrofuran to determine percent resin bound to sawdust. Onlysamples of 40% sawdust were extracted. The initial weight minus theretain after extraction--the weight of the sawdust gives the amount ofresin attached to the wood.

    ______________________________________                                        Soxhlet Extraction Data                                                       Composite with Percent                                                        40% sawdust    resin retain                                                   ______________________________________                                        10% VERR-40    5.6                                                            4% VERR-40     2.6                                                            10% SMA #1     7.4                                                            Control        1.0                                                            ______________________________________                                    

Fusion bowl data confirm the covalent reaction between wood fiber andSMA #1 resin. An increase in the equilibrium torque shows substantialreaction. In case 1, no fiber is used. In case 2, fiber is combined withno reactive resin and polystyrene a nonreactive resin. The equilibriumtorque in the presence of fiber and substantial quantities of reactiveSMA resin shows a 52% increase. Similar data is shown in case 3 usingfiber and a styrene maleic anhydride modifier material.

The following data shows that modified polyvinyl chloride polymer canalso improve physical properties of the composite material. Further, thedata shows the thermoplastic nature of the modified material. Themodified material can be formed in a modified state, ground andreprocessed under thermoplastic conditions with no substantial change inphysical properties.

    ______________________________________                                        Fusion Bowl Data                                                              Compound: PVC, TM181 1phr*, calcium stearate                                  1.5phr, oxidized polyethylene, 0.8phr, Paraffin 0.8phr                                                          %                                           Additive       AWF        Eq. Tqe Increase                                    ______________________________________                                        Case 1                                                                        --             --         2135    0.00                                        (1) 10% SMA 332                                                                              --         2182    2.20                                        10% PS         --         1598    -25.15                                      Case 2                                                                        --             40% Dried  1795    0.00                                        (1) 10% SMA 332                                                                              40% Dried  2730    52.09                                       10% PS         40% Dried  1891    5.35                                        Case 3                                                                        --             40% Dried  1883    0.00                                        (1) 10% SMA 332                                                                              40% Dried  3799    101.75                                      (3) 10% PolySci                                                                              40% Dried  3926    108.50                                      SMA                                                                           ______________________________________                                         * phr = parts per hundred parts resin                                    

Fusion Bowl Operation:

Fusion bowl is a Brabender mixer of the type 6 with roller blades. Themixer was heated to 185° C. A charge of 62 grams was fed into the mixerwith the blades rotating at 65 rpm. Automatic data acquisition softwarefacilitated continuous recording of torque and material temperature. Anychemical interaction such as bonding between the compatibilizer and thesawdust results in an increase in the torque. Too much reaction wouldincrease the torque and thus the temperature to an extent that PVCdegrades. PVC degradation shows up as discoloration to black and alsoHCL fumes. Thus the fusion bowl can be used to monitor reactions betweenvarious ingredients.

Vinyl Chloride Terpolymer

A conventional polyvinyl chloride wood fiber composite as shown above inthe comparative examples was modified using a vinyl chloride/vinylacetate/vinyl alcohol #3 terpolymer (91%-3%-6% by mole) MW=70,000,coupled with a diglycidyl bisphenol A (DERR 332). The following datatable shows the presence of the terpolymer improves tensile stress withno substantial loss in modulus.

    ______________________________________                                        (3)                                                                           Terpolymer                                                                              Modulus       Elongation                                                                             Stress                                       ______________________________________                                        0         1045094       1.173    5896                                         3         1056674       1.054    6637                                         5         1046822       1.121    6351                                         8         1027874       1.155    6452                                         10        1047205       1.096    6715                                         0         1047415       1.121    6206                                         3         1039648       1.034    6421                                         5         1069781       1.037    6909                                         8         1052043       1.056    7237                                         ______________________________________                                    

We have found that an increase in impact strength is obtained by addinga compatibilizing agent containing a rubber molecule moiety. Thematerial is terpolymer as above coupled with the rubber and polymer withand epoxy diamine HYCAR1300X45 terminated butadiene acrylonitrile rubbercomponent HYCAR1300X45. The use of the rubber containing chemicalmodifier substantially increases the impact strength.

    ______________________________________                                                                        Impact                                        Terpolymer  Epoxy        TEA    Strength                                      ______________________________________                                        6           5.64         0       8.0/0.6                                      6           5.64         15                                                   (6) 1% ATBN,                                                                  applied                                                                       to sawdust                                                                    6           5.64         0                                                    6           5.64         15     10.4/0.4                                      ______________________________________                                    

Similarly, the materials shown in the table below were manufactured andrecycled as shown. Pass 1 shows that the modified material has a similartensile stress elongation and modulus as the other materials in thetable. Pass 2 is a second extrusion of the material of pass 1. Thephysical properties are not different significantly showing substantialthermoplastic character.

    ______________________________________                                                                                Tensile                               Terpolymer                                                                            Epoxy    TEA     Modulus                                                                              Elongation                                                                            Stress                                ______________________________________                                        0       0        0       1033518                                                                              1.08    5826                                  0       0        0       1036756                                                                              1.056   5889                                  5       0        0       1045985                                                                              1.049   6325                                  Pass 1  3        15      1073853                                                                              0.98    7001                                  Pass 2  3        15      1098495                                                                              1.007   7150                                  5                                                                             ______________________________________                                    

Similarly, a terpolymer comprising vinyl chloride vinyl acetate andvinyl alcohol is coupled with the polymer using an epoxy functionalityVERR40 (1.8 wt %). The use of such a material as a polymer modifierresults in a substantial increase in tensile strength. Data supportingthis conclusion is shown in the following table.

    ______________________________________                                        (3)      (4)     (5)            Elongation                                                                            Stress                                Terpolymer                                                                             Epoxy   TEA     Modulus                                                                              at max load                                                                           max load                              ______________________________________                                        0        0       0       1048353                                                                              1.114   5990                                  0        0       15.sup. 1059081                                                                              1.032   6233                                  0        4       --       994857                                                                              1.07    5735                                  0        4       15%     1089991                                                                              0.997   6500                                  6        0       --      1059950                                                                              1.084   6610                                  6        0       15%     1054579                                                                              1.04    6895                                  3        3       --      1104357                                                                              1.059   6174                                  3        3       15%     1142600                                                                              0.988   6701                                  5        3       --      1092483                                                                              0.998   6299                                  5        3       15%     1106976                                                                              0.979   6952                                  8        3       --      1104892                                                                              1.005   6438                                  8        3       15%     1126601                                                                              0.988   7093                                  8        5       --      1288699                                                                              0.908   6497                                  8        5       15%     1111775                                                                              0.907   7123                                  5        5       --      1137586                                                                              0.963   6383                                  5        5       15%     1115420                                                                              0.923   7105                                  3        5       --      1110601                                                                              0.972   6163                                  3        5       15%                                                          ______________________________________                                    

The foregoing disclosure provides an explanation of the compositions andproperties of the modified Thermoplastic material. Many alterations,variations and modifications of the invention arising in the extrudedmaterial can be made by substitution of equivalent modifier materials,rearrangement of the compositions, variations of the proportions, etc.Accordingly, the invention resides in the claims hereinafter appended.

We claim:
 1. A composite pellet, capable of formation into a structuralmember, which pellet comprises a cylindrical extrudate having a radiusof about 1 to 5 mm, a length of about 1 to 10 mm;the pellet compositioncomprising:(a) a major proportion of a polymer comprising vinylchloride; (b) about 10 to 45 wt-% of chemically modified cellulosicfiber having a minimum thickness of 1 μm and a minimum length of 3 μmand a minimum aspect ratio of about 1.8; and wherein the fiber ischemically modified by a reagent that can covalently bond to acellulosic hydroxyl, the reagent having a moiety that is compatible withthe polymer, said fiber is dispersed throughout a continuous polymerphase and the tensile stress a failure is increased when compared to acomposite with unmodified fiber.
 2. The pellet of claim 1 wherein thepolymer comprises a polyvinyl chloride homopolymer.
 3. The pellet ofclaim 1 wherein the polymer comprises a polyvinyl chloride copolymer. 4.The pellet of claim 1 wherein the cellulosic fiber is wood fiber.
 5. Thepellet of claim 4 wherein the wood fiber comprises sawdust.
 6. Thepellet of claim 2 wherein the polymer has a number average molecularweight of about 90,000±50,000.
 7. The pellet of claim 4 wherein thecopolymer has a number average molecular weight of about 88,000±10,000.8. The pellet of claim 1 wherein the wood fiber has a fiber width ofabout 0.3 to 1.5 mm, a fiber length of about 1 to 10 mm and an aspectratio of about 2 to
 7. 9. The pellet of claim 1 wherein water comprisesabout 0.01 to 5 wt-% of the pellet.